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Grey Mold in Hydroponics · Hydroponics Daily

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  Hello and welcome back to Hydroponics Daily, your go-to podcast for everything soilless cultivation.
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  I'm your host, Dr Russell Sharp, and today we're talking about a disease or
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  a pathogen that shouldn't be as much of a problem in hydroponics as it is in outdoor cultivation.
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  However, it is still a big issue, especially in crops that are just about to
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  be harvested and crops that have been harvested,
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  so what we call post-harvest, which is really frustrating because
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  you can get your crop all the way you can spend months and months and months
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  growing it and then it can also come to this one pathogen which is grey mold
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  or more scientifically botrytis cinerea there are a few different types of botrytis
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  there's one specific to pea crops but botrytis cinerea is the catcher one that affects most crops.
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  It's a fungus and it thrives in moist conditions and can devastate hydroponic
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  crops from strawberries to ornamentals.
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  So let's dive into its biology, how it's spread, and the best control strategies
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  for indoor growers or glasshouse or polytunnel growers.
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  So the first thing to note is that it's a saprotrophic fungus.
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  This means that it feeds on decaying plant tissue, but it also can behave as
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  a necrotroph in that it just kills and feeds on living cells.
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  However, it will gain much more of a foothold and much easier if there is dead
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  decaying material lying around your greenhouse, your glass house, your grow room.
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  So it spreads via airborne spores and can cross infect multiple plant species.
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  So this is not like powdery milgey which is specific to one plant or one plant species.
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  This plant can go from your strawberries to your tomatoes to your hops and just hop around.
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  It survives on plant debris cuttings and
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  fallen petals so cleanliness is
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  next to godliness when it comes to controlling grey mold also
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  controlling humidity is very important it will loves
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  humidity is above 90% as a lot of fungi do
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  and leaf wetness and when the leaves are wet
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  for 8 to 12 hours that's different they're two different things
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  leaf wetness and humidity you can have wet leaves and
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  low humidity that's a thing and that but both
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  of those things will lead to petritus cool temperatures so this is not a fungus
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  that thrives at high temperatures 15 to 20 degrees celsius not sure what that
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  is in old money or american but that's pretty cool even by english standards
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  that supports the germination and infection cycles.
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  And then here's the real kicker. Rain splash and overhead irrigation are a really
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  easy way of the spores being dispersed.
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  Now, it doesn't just disperse in rain splash. It doesn't just fly into the air.
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  It can also come off runoff.
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  So if you've got plants that are on plastic sheeting or on concrete on the ground.
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  Then it can come out of the runoff and go in from one plant to the other.
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  And in ornamental nurseries
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  here in the uk professional ornamental nurseries that's called running
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  botrytis and that's really difficult to control in strawberry
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  polytunnels then that's the reason
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  why a lot of strawberry growers use polytunnels it's
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  not to increase the heat so much it's mainly just to
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  prevent rain splash and in
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  the uk we call these spanish tunnels because they don't
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  have sides to them so if they were there to to
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  create a micro environment and keep the heat
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  in then they would have sides on them obviously and that would
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  increase the temperature and the humidity but there there's no
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  sides on them because they don't want to increase the humidity and they just want
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  to prevent that rain splash so there's spanish tunnels
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  for strawberries you see them all along the hillsides in
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  like herefordshire going up the m6 in shropshire places
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  like this then you'll see that's what spanish tools are
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  there for and then they are you'll notice the plastic is
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  removed when the plants are not flowering and fruiting
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  and so that's to prevent damage and to
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  increase light levels and prevent algae growth on them so they're
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  just there to prevent gray mold really humidity and
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  airflow control is also important so you want to maintain humidity
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  below 80 anyway you're using
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  dehumidifiers and ventilation eliminate free
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  moisture droplets puts on the leaves and make sure.
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  There's air movement will help with that and prevents micro climates as well
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  so you might have a humid you might have a hygrometer that says it's 70% humidity
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  but if you've not got good air movement then you could have poor you could have
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  a micro climate one plant or one leaf could be much higher than that so that's so important to note.
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  As i said sanitation is critical remove dead leaves
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  petals and plant debris yes it will take time but
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  these are especially they get wet or they're
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  moist then they're not crispy these plant materials will
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  be producing gray mold spores disinfect
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  your tools surfaces and growing systems so your
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  growing systems you're going to be using something like hydrogen peroxide commercial cleaners
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  for the surfaces and for tools use
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  something like a strong vinegar or something like
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  that or a specialist cleaning implement
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  liquid quarantine protocols for all pests and diseases really i'm always saying
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  you know you've got to quarantine plant material coming in if you've got expensive
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  genetics or if the chances of a pest or a disease or something like thrips or
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  grey mold getting in is a big issue then obviously you want to quarantine and
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  prevent overcrowding as well so,
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  What do you do when you've got grey mould? Well, there are conventional fungicides you can use.
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  Strobilurins, they're a very common one. Depending on where you are,
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  what's registered for grey mould.
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  Iprodione, chlorothalonine, they can affect it, but face a couple of issues.
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  One, the grey mould can build up resistance to them.
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  And two, do you want to be applying a fungicide just before you harvest a crop?
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  If it's an edible crop or a smokable crop, things like this then you don't want
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  to be doing that in cut flowers they do do this they did roses for example are
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  commonly dipped in fungicide to prevent grey mold in once they've been harvested,
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  but obviously you've got fungicide pesticide residues on them so that's why
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  i always say wear gloves when you're handling roses and cut flowers because
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  they're dipped in fungicide before,
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  they um leave kenya and ecuador and
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  kunming a place like this and then you
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  there are certain plants that are
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  grouped together in their susceptibility to
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  certain strains of grey mould and you could if you're
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  on a nursery that was growing lots of different types of plants you could
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  group them together and prevent and delay resistance you could
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  look at applying different fungicides at
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  different times as well to prevent resistance building up rather than
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  just relying on one fungicide as you consider there are
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  some biological um control methods trichoderma particularly
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  trichoderma has a has harzianum that's
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  easy for me to say can reduce botrytis through competition.
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  And antagonism that's a free living
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  fungus that is in a lot of mycorrhizal products trichoderma
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  harzianum chitosan formulations
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  activate plant defenses degrade fungal cell walls and
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  prevent infection so they're promising for hydroponic setups the
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  beauty of chitosan is that it's non-toxic unlike the other
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  fungicides so it's a biofungicide so we definitely
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  recommend use of chitosan certain yeasts and
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  epiphytic fungi have shown strong grey mold
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  suppression nearly matching chemical fungicides in
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  trials so that's where like brewers yeast
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  and things like this that could be a good source of spray
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  but obviously you need to make sure you know what you're doing
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  with those things the other part to consider is that
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  there are certain insects that can act as vectors
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  so a vector is a is an organism or anything
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  it's a thing that transfers one
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  biological organism to another so if you think of bees for pollen they're a
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  vector if you think of aphids they're a vector for viruses and but so are secateurs
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  so they're a vector and then when it comes to grey mold fungus gnats midges
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  and even slugs can spread spores between plants so.
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  Making sure you get control of your insects is very important,
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  even if the pest numbers are low.
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  Control them through sticky traps, make sure you control fungus gnats using
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  a variety of different methods, and things like that.
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  So another useful method that is becoming even more popular is UV irradiation.
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  And UVC, so about 254 nanometers, can effectively inactivate botrytospores in
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  the air and on the surface.
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  So they have been used uvc radiators what's
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  the word lights light arrays are being used now
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  on commercial strawberry farms to kill off
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  botrytis so they go in after the workers have been there because
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  obviously uvc is highly toxic to humans it will
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  cause cancer and cataracts so you have to make sure no one's around
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  exposed to it and it will it will control
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  botrytis fairly effectively there's a few companies looking
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  at that now i think saga robotics so they got
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  one that's one company uh uvb and blue
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  lights they have complex effects so uvb can stimulate
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  sporulation but blue light can suppress it
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  so play around with uvb lights
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  if you've got a uvb light and i wouldn't mess around with uvc
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  unless you know what you're doing unless you're in an unoccupied room uvc in
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  like air ducts and filters can be an option there's a few filters that have
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  uv built into them to control spores coming into the gray room let's have a
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  look at the plants that are really susceptible So strawberries, as I've said,
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  geraniums, so pelagoniums as they're also known, cyclamen, cyclamen really,
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  that's the one that gets running botrytis on nurseries, primula,
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  primroses, and ornamentals like roses.
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  They are the main ones that get botrytis.
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  And botrytis strains can often infect a range of unrelated hosts.
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  So if you've got plants in the garden that have got botrytis,
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  the spores might come into your groan through the inlet fan, unfortunately.
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  And as always an integrated management strategy is
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  best so integrated pest management
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  or integrated pest and disease management IPM so in
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  summary control the humidity use tunnels if you're a strawberry grower make
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  sure you've got good airflow so don't have walls on your tunnels make sure you've
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  got fans if you're going in an aquarium daily removal of dead leaves and any
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  dead plant material especially like rotting tomatoes or strawberries on the
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  plants if they're rotting remove them,
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  sterilise your grow room once all the plants are out and you're going for a
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  new grow deploy trichoderma, chitosan even beneficial yeasts,
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  things like this if you're interested in biocontrol if you're going to use a
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  fungicide make sure you rotate them and prevent dip.
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  And if you're going to use cut flowers, make sure you know that they're dipped in fungicides.
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  And if you're a big grower, then you could look at UVC irradiation.
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  However, if you're a small grower, I'd be very careful of that because,
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  as I say, it can cause cataracts and cancer.
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  If you are exposed to too much of it or any of it, because it's non-natural,
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  it doesn't exist in the Earth's surface.
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  It is, what's the word, intercepted by the Earth's atmosphere.
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  So unless you're an astronaut, you're not going to be exposed to UVC or if you're
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  on a strawberry farm that's using UVC to control it.
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  So hopefully they are following all the best practice on those and they're not
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  exposing workers to UVC.
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  So we said grey mould thrives in hydroponic conditions, but with proactive planning,
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  your crops can thrive without it.
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  So as I say, it's one that's really going to be a kicker because it can hit
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  once your crop's been harvested or just before harvest.
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  So be aware of grey mould. Make sure you know the symptoms, which is obviously
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  just a grey, really like fluffy growth on your plants, on the leaves.
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  There will also be a human health hazard with grey mould because of all those spores.
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  If you disturb a load of leaf material that's got grey mould on it,
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  then you could get a big lung full of spores.
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  And that, although not toxic in itself, when you inhale spores in high volumes,
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  you get something called farmer's lung which is a
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  debilitating disease so don't
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  get farmer's lung if you've found this interesting then
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  please look at your phone now and if you're on especially if you're on apple
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  podcasts and you're listening to it click onto the podcast for hydroponics daily
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  and click the plus side to follow that would be a big help and you wouldn't
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  get any you wouldn't miss a single episode of this absolute babbling drivel.
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  And yeah, you can listen to other amazing podcasts, episodes about other horrible
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  pathogens that could ruin your day.
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  Thank you very much for listening. We'll do something exciting and interesting
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  and positive tomorrow. Until then, goodbye.